The confidential filing was made under the JOBS act, allowing the company to work with regulators on its plans before making them public. The S-1 will have to be made public at least 21 days before the company starts it "roadshow" to convince large investors to participate.

A company has to have less than $1 billion in revenue to file in secret. It is on track to post $583 million in revenue in 2013, according to advertising consultancy eMarketer.

Twitter did not have to disclose they made the filing but chose to do so.

Shares of Twitter, which filed for an initial public offering, could be interesting, but only at the right level, Dan Niles of Alpha One Capital says.

Twitter's revelation comes just days after Facebook shares fully recovered from the plunge they suffered after that company's troubled IPO in May 2012 to reach an all-time high. As of Thursday's close, Facebook is up 17.8 percent from its $38 offering price.

CEO Mark Zuckerberg, who had said companies should avoid going public for as long as possible, softened this week. "In retrospect, I was too afraid of going public...you have to stay focused on doing the right stuff," he said Wednesday at the TechCrunch Disrupt conference.

Other social media stocks have done even better. LinkedIn has soared to almost $250 a share from its $45 offering price in May 2011.

Yelp is up 325 percent since its March 2012 IPO, although Groupon is down more than 41 percent since it went public in November 2011.

Twitter's IPO, though much smaller than Facebook's, could still generate tens of millions of dollars in fees from the underwriting mandate itself.

Assuming the company sells around 10 percent of its shares, or $1 billion, underwriters could stand to divide a fee pool of $40 million to $50 million, assuming an overall fee cut of 4 percent to 5 percent, according to Freeman & Co.